The structure, function, and subcellular location of a low molecular weight, high affinity calcium-binding protein will be elucidated. Structural studies will include fluorometric and ultraviolet absorption spectral measurements in the presence and absence of calcium, titration of the phenolic hydroxyl groups, competitive binding experiments with various ions and drugs, complete amino acid composition, and tryptic peptide mapping. Functional studies will include determination of the protein's ability to activate cAMP phosphodiesterase under a variety of conditions, as well as its activation or inhibition of protein kinases and adenylate cyclase. Location studies will include attempts to produce precipitating antibodies to the protein.